LeetCode - Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.

Note: A leaf is a node with no children.

Example:

Given the below binary tree and sum = 22,

      5
     / \
    4   8
   /   / \
  11  13  4
 /  \    / \
7    2  5   1
Return:

[
   [5,4,11,2],
   [5,8,4,5]
]

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<List<Integer>> pathSum(TreeNode root, int sum) {
        List<List<Integer>> resList = new ArrayList<List<Integer>>();
        if (root == null) {
            return resList;
        }
        List<Integer> aList = new ArrayList<Integer>();
        aList.add(root.val);
        helper(root, resList, aList, root.val, sum);
        return resList;
        
    }
    
    public void helper (TreeNode node, List<List<Integer>> resList, List<Integer> aList, int currentSum, int sum) {
        if (node.left == null && node.right == null){
            if (currentSum == sum) {
                resList.add(aList);
            }
            return;
        }
        if (node.left != null){
            List<Integer> leftList = new ArrayList<>(aList);
            leftList.add(node.left.val);
            helper(node.left, resList, leftList, currentSum+node.left.val, sum);
        }
        if (node.right != null){
            List<Integer> rightList = new ArrayList<>(aList);
            rightList.add(node.right.val);
            helper(node.right, resList, rightList, currentSum+node.right.val, sum);
        }
        return;
    }
}